Veneer cutting machines are used to cut out defective sections of large sheets of wood veneer. The veneer sheets are fed to the cutting machine by means of rollers or conveyor belts. Before a veneer sheet reaches the cutting machine, it passes under a defect scanner that locates defects in the veneer sheet. As the veneer sheet reaches the cutting machine, the defect scanner signals one or more blades to cut the sheet both in front of and behind the defect. After the sheet leaves the cutting machine the excised defective section is removed.
A veneer cutting machine must be capable of making a transverse cut across a sheet of veneer as the veneer sheet is moving along the rollers or conveyor belt. Older prior art machines dropped a weighted blade, similar to a guillotine, or used a motorized chopping blade to make the cut. This type of cutting resulted in a momentary stopping of the veneer sheet as well as frequent binding between the wood and the blade as the blade was withdrawn. To avoid this binding, the sheets of veneer were moved at very slow speeds. More recent cutting machines utilize a rotating blade that moves with the veneer sheet as the blade is cutting. Successive cuts can either be made by the same blade or by two separate rotating blades. In either case, rotating blades permit faster movement of the veneer sheet as it is being cut. While the speed of the rotating blade is related to the mass of the blade assembly, use of lighter materials to construct the relatively long blade assemblies results in a flexing at the center portion of the blade assembly. This flexing prevents a clean cut from being made across the veneer sheet. A backup roller positioned above the rotating blade assembly is used to prevent flexing. An additional backing member is located underneath the veneer sheet to provide a cutting surface for the blade. In the past, backing members have usually consisted of large, heavy rotating rollers that also assist in movement of the veneer sheets as they are being cut. The disadvantage of backing rollers is that they are expensive to maintain and cumbersome to change. Another disadvantage to using backing rollers is the difficulty in finely aligning the roller with the blade to maintain uniform pressure between the blade and the cutting surface of the roller.